IAEA/AQ/56
IAEA Analytical Quality in Nuclear Applications Series No. 56
Worldwide Interlaboratory
Comparison on the Determination of Trace Elements
in Oyster Biota Sample IAEA-470
INTERNATIONAL ATOMIC ENERGY AGENCY VIENNA
ISSN 2074–7659 Template has: 20 mm spine
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WORLDWIDE INTERLABORATORY COMPARISON ON THE
DETERMINATION OF TRACE ELEMENTS
IN OYSTER BIOTA SAMPLE IAEA-470
AFGHANISTAN ALBANIA ALGERIA ANGOLA
ANTIGUA AND BARBUDA ARGENTINA
ARMENIA AUSTRALIA AUSTRIA AZERBAIJAN BAHAMAS BAHRAIN BANGLADESH BARBADOS BELARUS BELGIUM BELIZE BENIN
BOLIVIA, PLURINATIONAL STATE OF
BOSNIA AND HERZEGOVINA BOTSWANA
BRAZIL
BRUNEI DARUSSALAM BULGARIA
BURKINA FASO BURUNDI CAMBODIA CAMEROON CANADA
CENTRAL AFRICAN REPUBLIC CHADCHILE CHINA COLOMBIA CONGO COSTA RICA CÔTE D’IVOIRE CROATIA CUBACYPRUS
CZECH REPUBLIC DEMOCRATIC REPUBLIC
OF THE CONGO DENMARK DJIBOUTI DOMINICA
DOMINICAN REPUBLIC ECUADOR
EGYPT EL SALVADOR ERITREA ESTONIA ESWATINI ETHIOPIA FIJIFINLAND FRANCE GABON GEORGIA
GERMANY GHANA GREECE GRENADA GUATEMALA GUYANA HAITI HOLY SEE HONDURAS HUNGARY ICELAND INDIA INDONESIA
IRAN, ISLAMIC REPUBLIC OF IRAQIRELAND
ISRAEL ITALY JAMAICA JAPAN JORDAN KAZAKHSTAN KENYA
KOREA, REPUBLIC OF KUWAIT
KYRGYZSTAN
LAO PEOPLE’S DEMOCRATIC REPUBLIC
LATVIA LEBANON LESOTHO LIBERIA LIBYA
LIECHTENSTEIN LITHUANIA LUXEMBOURG MADAGASCAR MALAWI MALAYSIA MALIMALTA
MARSHALL ISLANDS MAURITANIA
MAURITIUS MEXICO MONACO MONGOLIA MONTENEGRO MOROCCO MOZAMBIQUE MYANMAR NAMIBIA NEPAL
NETHERLANDS NEW ZEALAND NICARAGUA NIGER NIGERIA NORWAY OMANPAKISTAN
PALAU PANAMA
PAPUA NEW GUINEA PARAGUAY
PERUPHILIPPINES POLAND PORTUGAL QATAR
REPUBLIC OF MOLDOVA ROMANIA
RUSSIAN FEDERATION RWANDA
SAINT VINCENT AND THE GRENADINES SAN MARINO SAUDI ARABIA SENEGAL SERBIA SEYCHELLES SIERRA LEONE SINGAPORE SLOVAKIA SLOVENIA SOUTH AFRICA SPAIN
SRI LANKA SUDAN SWEDEN SWITZERLAND
SYRIAN ARAB REPUBLIC TAJIKISTAN
THAILAND
THE FORMER YUGOSLAV REPUBLIC OF MACEDONIA TOGOTRINIDAD AND TOBAGO TUNISIA
TURKEY
TURKMENISTAN UGANDA UKRAINE
UNITED ARAB EMIRATES UNITED KINGDOM OF
GREAT BRITAIN AND NORTHERN IRELAND UNITED REPUBLIC
OF TANZANIA
UNITED STATES OF AMERICA URUGUAY
UZBEKISTAN VANUATU
VENEZUELA, BOLIVARIAN REPUBLIC OF
VIET NAM YEMEN ZAMBIA ZIMBABWE The following States are Members of the International Atomic Energy Agency:
The Agency’s Statute was approved on 23 October 1956 by the Conference on the Statute of the IAEA held at United Nations Headquarters, New York; it entered into force on 29 July 1957.
The Headquarters of the Agency are situated in Vienna. Its principal objective is “to accelerate and enlarge the contribution of atomic energy to peace, health and prosperity throughout the world’’.
IAEA/AQ/56 IAEA Analytical Quality in Nuclear Applications Series No. 56
WORLDWIDE INTERLABORATORY COMPARISON ON THE
DETERMINATION OF TRACE ELEMENTS IN OYSTER BIOTA SAMPLE IAEA-470
INTERNATIONAL ATOMIC ENERGY AGENCY VIENNA, 2018
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WORLDWIDE INTERLABORATORY COMPARISON ON THE DETERMINATION OF TRACE ELEMENTS IN OYSTER BIOTA SAMPLE IAEA-470
IAEA, VIENNA, 2018 IAEA/AQ/56 ISSN 2074–7659
© IAEA, 2018 Printed by the IAEA in Austria
December 2018
FOREWORD
The primary goal of the IAEA Environment Laboratories is to help Member States understand, monitor and protect the marine environment. Thus, the major impact on marine ecosystems exerted by large coastal cities is an issue of primary concern for the IAEA and its Member States.
Marine pollution assessments depend on accurate knowledge of contaminant concentrations in various environmental compartments. Since the early 1970s, the IAEA Environment Laboratories have been assisting national laboratories and regional laboratory networks in the analysis of radionuclides, trace elements and organic contaminants in marine samples through global interlaboratory comparisons and regional proficiency tests, the production of marine certified reference materials and the development of analytical methods for analysing trace elements and organic pollutants in marine samples. The Marine Environmental Studies Laboratory in Monaco, part of the IAEA Environment Laboratories, actively assists Member States in organizing interlaboratory comparisons designed to monitor and demonstrate the performance and analytical capabilities of the participating laboratories, and to identify gaps and problem areas where further developments are needed.
The present publication summarizes the results of the IAEA-470 interlaboratory comparison on the determination of trace elements in oyster sample.
The IAEA wishes to thank the Korea Institute of Science and Technology for providing the raw sample material. The IAEA is also grateful to the the Government of Monaco for its support.
The IAEA officers responsible for this publication were S. Azemard and E. Vasileva of the IAEA Environment Laboratories.
EDITORIAL NOTE
This publication has been prepared from the original material as submitted by the contributors and has not been edited by the editorial staff of the IAEA. The views expressed remain the responsibility of the contributors and do not necessarily reflect those of the IAEA or the governments of its Member States.
Neither the IAEA nor its Member States assume any responsibility for consequences which may arise from the use of this publication.
This publication does not address questions of responsibility, legal or otherwise, for acts or omissions on the part of any person.
The use of particular designations of countries or territories does not imply any judgement by the publisher, the IAEA, as to the legal status of such countries or territories, of their authorities and institutions or of the delimitation of their boundaries.
The mention of names of specific companies or products (whether or not indicated as registered) does not imply any intention to infringe proprietary rights, nor should it be construed as an endorsement or recommendation on the part of the IAEA.
The IAEA has no responsibility for the persistence or accuracy of URLs for external or third party Internet web sites referred to in this publication and does not guarantee that any content on such web sites is, or will remain, accurate or appropriate.
CONTENTS
1. INTRODUCTION ... 1
2. SCOPE OF THE INTERLABORATORY COMPARISON ... 1
3. DESCRIPTION OF THE MATERIAL ... 2
4. EVALUATION OF ANALYTICAL PERFORMANCE ... 4
5. RESULTS AND DISCUSSION ... 4
5.1. Overview of the results ... 4
5.2. Laboratory performances ... 5
5.3. Analytical methods ... 13
5.4. Sample treatment, impact of water content, use of crm and recovery corrections .... 14
6. RECOMMENDATIONS ... 15
7. CONCLUSIONS ... 15
APPENDIX I ... 17
APPENDIX II ... 41
REFERENCES ... 61
LIST OF PARTICIPANTS ... 63
CONTRIBUTORS TO THE DRAFTING AND REVIEW ... 69
1 1 INTRODUCTION
The Marine Environmental Studies Laboratory (MESL) of the IAEA’s Environment Laboratories (IAEA-NAEL) has the programmatic responsibility to provide assistance to Member States’ laboratories in maintaining and improving the reliability of analytical measurement results, both in trace elements and organic pollutants. This is accomplished through the provision of certified reference materials of marine origin, validated analytical procedures, training in the implementation of internal quality control, and through the evaluation of measurement performance by the organization of worldwide and regional interlaboratory comparisons. IAEAs subprogram ‘Reference Products for Science and Trade’
represents an important benchmark in upgrading the quality of laboratory performances and assessing the validity of the analytical methods used for marine monitoring studies in the IAEA Member States.
For more than thirty years, the MESL has conducted worldwide laboratory performance studies, also known as interlaboratory comparison [1, 2]. The results have been used to evaluate laboratory performance with respect to a wide range of organic [3, 4] and inorganic pollutants, including methylmercury [5, 6].
The goal of interlaboratory comparison is to demonstrate the measurement capabilities of laboratories participating in interlaboratory comparisons (ILCs) and targeted proficiency tests (PTs). The results from ILCs or PTs are of crucial interest for laboratories as they provide clear information of their measurement capabilities. NAEL Interlaboratory Comparison (ILC) and Proficiency Test (PT) schemes involve comparison of participant’s results with an assigned value, which usually is delivered as a consensus value from the overall population of reported by participating laboratories test results.
These exercises are designed to monitor and demonstrate the performance and analytical capabilities of the participating laboratories, and to identify gaps and problem areas where further development is needed.
2 SCOPE OF THE INTERLABORATORY COMPARISON
The present interlaboratory comparison was designed to evaluate the measurement performance of participating laboratories for the analysis of trace elements in marine biota sample (oyster).
Invitation letters have been sent to 39 laboratories, previously participated in an IAEA ILC.
Positive responses were received from 34 laboratories in 20 Member States and samples were duly dispatched to them.
Each participating laboratory received one bottle of the marine biota material, accompanied by an information sheet and a reporting form. Using the procedures, routinely applied in their laboratories, participants were requested to determine as many elements as possible from the following list: copper, cadmium, lead, lithium, zinc, mercury, methyl mercury nickel, vanadium, arsenic, silver, aluminium, iron, manganese, chromium, cobalt, tin and strontium.
The organisers were also interested in receiving results for any other elements that the participating laboratories were willing to provide.
In total 30 laboratories (reporting 34 datasets) from 19 countries participated in this ILC and reported results for 35 elements.
2
The data reported by the laboratories, together with the technical and statistical evaluations of the results for each element, are included in this report. All results were treated confidentially and each laboratory was identified with a code number for anonymity.
3 DESCRIPTION OF THE MATERIAL
The interlaboratory comparison sample, distributed in this exercise was a Certified Reference Material (CRM) IAEA-470. All details about homogeneity, stability and characterization can be found in the certification report [7].
Reported measurement results were first evaluated with Kernel density plots [8]. Certified mass fraction values for selected trace elements and methylmercury, used in the evaluation process of reported results are shown in Table 1.
The assigned values for 5 additional elements, not included in Table 1, were calculated as described in the ISO 13528 standard, Annex C.21 [9]. Calculated robust mean and robust standard deviations are presented in Tables 2 and 3.
The uncertainties associated with the assigned values were calculated according to the ISO 35 standard [10]. The relative combined uncertainty of the assigned value of the CRM consists of uncertainty related to the characterization (uchar), between bottle heterogeneity (uhom) and long–
term stability (ustab). Above mentioned contributions were combined to estimate the expanded uncertainty, as described in the Eq. (1).
𝑈 = 𝑘 × 𝑢 + 𝑢 + 𝑢 (1)
Where k: coverage factor 2, representing a level of confidence of about 95%.
uhom – uncertainty on homogeneity of oyster sample is set at 3.5% and the estimation is based on the obtained results from homogeneity study.
ustab - uncertainty on stability during the storage period was estimated at 3.5%.
More details on stability and homogeneity study for the IAEA-470 sample are described in the certification report [7].
uchar – uncertainty on characterisation of oyster sample are calculated following the Eq. (2)
𝑢 = 1.25 × ∗
√ (2)
Where s* is the robust standard deviation, calculated as described in the IS0 13528 [9] and n is the number of datasets used for calculation of the robust mean.
For Al and Ni obtained expanded uncertainties were higher than 25%. The reasons for the high uncertainties were the broad distribution of reported data for Al and insufficient homogeneity for Ni [7], respectively. As a consequence, those values were given as informative values and were not used for the evaluation of measurement performances of laboratories, participating in the IAEA-470 interlaboratory comparison.
3 TABLE 1. CERTIFIED VALUES FOR THE IAEA-470 OYSTER CRM
Element Unit Certified value1 Expanded uncertainty
(k=2)2
Ag mg kg-1 1.29 0.10
As mg kg-1 11.9 0.9
Ca mg kg-1 2430 282
Cd mg kg-1 3.14 0.24
CH3Hg µg kg-1 as Hg 5.22 0.87
Co mg kg-1 0.201 0.025
Cr mg kg-1 0.965 0.113
Cu mg kg-1 146 13
Fe mg kg-1 131 12
Hg µg kg-1 21.1 2.1
Mg mg kg-1 3080 390
Mn mg kg-1 66.7 5.3
Na mg kg-1 19.7 103 2.3 103
Pb mg kg-1 0.361 0.053
Rb mg kg-1 5.14 0.59
Se mg kg-1 3.06 0.33
Sr mg kg-1 20.6 1.6
V mg kg-1 0.899 0.130
Zn mg kg-1 727 48
TABLE 2. ASSIGNED VALUE FOR THE IAEA-470 OYSTER SAMPLE
Element Unit Assigned value1 Expanded uncertainty
(k=2)2
K mg kg-1 12720 2150
Li mg kg-1 0.532 0.094
TABLE 3. INFORMATIVE VALUE IN IAEA-470 OYSTER SAMPLE
Element Unit Informative value1 Expanded uncertainty
(k=2)2
Al mg kg-1 72.9 19.9
Ni mg kg-1 0.849 0.291
4
4 EVALUATION OF ANALYTICAL PERFORMANCE
The individual laboratory performance was expressed in terms of z-score and Zeta-score, in accordance with the ISO 13528 [9].
The determination of target standard deviation was done on the basis of the outcome from the previous ILCs organised by the MESL for the same population of laboratories and similar sample matrix. The standard deviation for the proficiency assessment, σp, was fixed to 12.5 % from the assigned values. The appropriateness of this level of variability of results was confirmed by calculation of the robust standard deviation of the participants’ results and the uncertainty of the assigned values for the respective measurants.
z-score, calculated following the Eq. (3), effectively expresses the difference between the mean of the laboratory and the assigned value in units of target standard deviation (p).
Zeta-score, calculated according to the Eq. (4), indicates the agreement of the result of the individual participant with the ILC assigned value within the respective uncertainties. The denominator in the Eq. (4) is calculated from the combined uncertainty of the assigned value and the measurement uncertainty reported by the participating laboratory.
𝑧 = (3)
Zeta = (4)
Where:
lab : Reported results by participant (express as the mean of multiple determination) xref: Certified value or assigned value
p: Target standard deviation
uxlab: Standard uncertainty reported by participant
uref: Standard uncertainty of certified (or assigned) value
The interpretation of a laboratory’s performance was evaluated according to the following generally accepted limits:
│ z or Zeta│ ≤2 Satisfactory 2< │ z or Zeta│ <3 Questionable
│ z or Zeta│3 Unsatisfactory
5 RESULTS AND DISCUSSION 5.1 OVERVIEW OF THE RESULTS
Thirty laboratories provided results for the analysis of the IAEA-470 oyster sample by the final deadline. Thirty-three sets of measurement results were submitted (some laboratories reported
5 data generated by multiple techniques) comprising 407 results for 35 different elements. z- scores and Zeta-scores were evaluated only for 21 elements.
From the 21 elements evaluated, 11 elements (As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Pb, V and Zn) have been reported by more than 50% of participants.
For elements with more than 5 reported datasets, graphical presentations of z-score and Zeta- scores (except for Al and Ni) are presented in Appendix I, together with a Kernel density plot (if more than 8 data have been reported) and short summary on the statistical evaluation of results for the reported elements [8].
All reported data are presented in the Appendix II. For editorial purposes some results have been rounded to appropriate number of significant figures.
5.2 LABORATORY PERFORMANCES 5.2.1 z-scores:
Table 4 shows the z-scores of laboratories for all reported elements. The overall performance (z-scores) of participating laboratories is graphically presented on Figures 1 and 3.
The z-score compares the participant’s deviation from the reference value with the target standard deviation (p for proficiency assessment). p is defined by the ILC organizer as the maximum acceptable standard deviation (25% in this case) of the assigned value for the investigated trace elements.
In total from the calculated 352 z-scores, 93% were │z│ ≤ 2, 96% │z│ < 3, and only 3% were considered as unsatisfactory with │z│ > 3.
Among 33 datasets, 17 (52%) were with │z│ ≤ 2 for all reported results and 25 (76%) with
│z│ < 3. All participants reported at least 50% of their measurement results with │z│ ≤ 2.
As shown on Figure 3 the part of accepted measurement results was 65% or higher for each of the evaluated elements. Methyl mercury, total mercury and lead appeared to be the elements reported with the highest number of unsatisfactory z-scores. This shows that the accurate determination of those elements in biological material is still challenging analytical task, particularly at low mass fraction levels.
This is underlined by the fact that a large part (72% ) of │z│ > 3 is positive, demonstrating positive bias. These biased results may arise from the contamination during sample preparation (e.g., digestion) step or from the instrumental steps. The laboratories concerned should carefully check sample preparation procedures (e.g., quality chemical reagents used) and try to improve their working laboratory environment. Laboratories should also develop an effective scheme for cleaning of the lab ware and regularly control this process.
Erroneous calibration standards could be another source of bias. It is important to note that losses in the working standard solutions at low concentration level can be the reason for the overestimation of the concentrations of investigated elements. Only standard solutions (CRMs) with stated SI traceability should be used for calibration purposes and in addition they should not be stored for an extended period of time.
Laboratories with questionable and unsatisfactory results should also carefully check all analytical procedures, laboratory equipment and instrumentation.
6
5.2.2 Zeta-scores:
Table 5 shows the overall performance (Zeta-scores) of laboratories for different trace elements.
The overall performance (Zeta-scores) of participating laboratories are graphically presented on Figures 2 and 4.
The Zeta-score shows the level of agreement of the laboratory result with the assigned value within the respective uncertainties. The denominator in the Eq. (2) is the combined uncertainty of the assigned value and the uncertainty of measurement result, reported by the individual laboratory.
Five laboratories (15%) didn’t report uncertainties and Zeta-scores for their results were not calculated.
As it can be easily seen in Figures 1 and 2, the comparison of laboratories performances evaluated with z-score and Zeta-score clearly indicate that the number of unsatisfactory Zeta- scores is considerably higher than the number of unsatisfactory z-scores (3% for z-scores and 8% for Zeta-scores). Only 10 laboratories (30%) could report 100% of their results with │z│
and │Zeta-scores ≤ 2. As the Zeta-score is the parameter, reflecting all parts of the measurement procedure, laboratories with unsatisfactory Zeta-scores should invest additional efforts in the proper evaluation of measurement uncertainty of reported measurement results. Overall, obtained results indicates that they are still remaining problems with the realistic estimation of measurement uncertainty.
If should be mentioned here that an unsatisfactory Zeta-score can be also caused by wrong estimation of the mass fraction of the respective trace element.
│z│ 3, 2< │z│ <3, │z│ ≤ 2
FIG. 1. The z-scores of results reported by the participants per laboratory.
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
20 27 23 32 3 18 10 6 14 8 2 5 30 16 26 28 1 4 7 9 12 13 15 17 19 25 31 33 34 35 36 22A 22B
7
│Zeta│ 3, 2< │Zeta│ <3, │Zeta│ ≤ 2
FIG. 2. The Zeta-scores of results reported by the participants per laboratory.
│z│ 3, 2< │z│ <3, │z│ ≤ 2
FIG. 3. The z-scores of results reported by the participants per element.
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
26 22B 4 23 32 18 33 28 14 5 10 6 16 7 25 8 1 2 9 12 13 15 19 31 34 35 36 22A
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
CH3Hg Hg Pb Co V Sr Cr Fe Cu Ag As Ca Cd K Li Mg Mn Na Rb Se Zn
8
│Zeta│ 3, 2 < │Zeta│ < 3, │Zeta│ ≤ 2
FIG. 4. The Zeta-scores of results reported by the participants per element.
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Hg CH3Hg Ag Sr Se Co Cd Pb Mn As Cr Fe Mg Cu Zn V Ca K Li Na Rb
9 TABLE 4. OVERALL ASSESSMENT OF LABORATORIES PERFORMANCE (z-SCORE) BY ELEMENTS Lab code AgAs Ca Cd CH3HgCo Cr Cu FeHgKLi MgMnNaPbRb SeSrVZn 1 0.47 0.63 0.08 -0.04 0.29 -0.11 0.37 -1.18 0.49 0.94 -0.47 1.75 0.19 0.51 2 0.11 0.31 0.45 0.48 2.12 0.35 -0.41 0.04 0.33 0.00 -0.83 0.33 0.19 0.69 0.32 3 -0.61 0.10 1.50 0.88 0.43 0.61 14.47 -1.38 -2.57 0.83 4 -0.94 -0.10 -1.55 -0.88 -0.53 -0.48 5 0.34 0.33 0.36 0.14 -0.08 -1.72 0.00 -0.37 -2.39 -0.13 -0.24 -0.13 0.26 -0.16 0.30 6 -0.07 -0.56 -0.16 0.00 2.24 -0.05 -0.62 -0.50 7 -1.77 0.47 0.14 0.31 0.28 -0.07 -0.41 0.07 -1.18 0.38 0.08 0.77 0.63 -0.71 -0.16 1.01 0.32 0.06 8 0.43 -0.09 -0.49 -3.09 -0.69 0.10 0.12 -0.45 -0.89 0.35 -0.02 0.41 0.32 8B -0.38 9 -0.87 -1.14 -0.62 -1.25 -0.16 -1.01 -0.82 -0.12 -0.04 -1.75 -0.29 -0.65 -0.13 -1.05 -0.12 -0.06 -1.32 10 -0.07 -0.54 -1.20 0.00 0.24 -0.20 12.61 -1.42 12 0.11 -0.91 13-0.33 -0.32 0.31 -0.09 0.00 -0.07 -0.46 0.14 0.20 -0.11 0.14 -0.22 -0.47 0.51 14 -0.47 0.35 -1.73 6.57 -1.04 -0.49 0.99 -0.35 0.44 -0.53 -0.42 0.17 15 0.58 0.39 0.81 1.96 0.18 -0.51 0.48 0.49 0.47 1.39 0.63 0.79 1.02 0.20 0.42 0.36 -0.04 0.58 0.56 16-0.25 -0.74 -0.40 0.38 -0.92 -0.97 0.38 0.24 -5.57 -0.87 -0.31 0.16 -0.31 -0.37 -0.82 -0.69 0.15 17 -1.35 0.48 1.35 0.17 -0.32 18 0.79 0.31 -0.06 -0.35 0.01 -0.23 2.30 1.05 1.70 2.54 0.18 0.36 190.12 0.23 0.58 -0.04 0.20 0.75 20 1.26 -2.39 22A-0.68 0.07 -0.76 0.21 -0.19 -0.04 -0.84 -0.30 22B -1.71 1.75 -0.33 -1.13 -1.01 -1.17 23 0.47 -0.10 0.62 3.08 251.12 0.07 -0.95 0.31 -0.96 -0.69 -0.44 0.23 0.25 0.37 -0.88 0.14 261.55 1.09 0.47 1.45 2.90 0.73 -0.02 0.82 1.36 1.47 1.58 1.34 0.43 1.65 1.61 0.53 0.95 27 -1.50 6.13 6.73 0.12 -2.73 -1.77 5.27 -1.72 -3.12 -0.35 -1.14
10
TABLE 4. OVERALL ASSESSMENT OF LABORATORIES PERFORMANCE (z-SCORE) BY ELEMENTS (cont.) Lab codeAgAsCa Cd CH3Hg Co Cr Cu FeHgKLi MgMnNaPb Rb SeSrVZn 28-0.56 -0.85 -0.12 -0.32 -0.84 0.35 -0.51 2.30 -0.35 -0.54 0.92 -0.19 -0.78 -0.08 -1.43 -1.09 -0.67 -0.17 -0.39 30 1.75 0.16 0.00 3.80 -1.23 0.16 -0.31 -0.53 0.61 -0.05 0.07 0.97 0.42 0.34 -0.12 -0.10 31 -0.18 -0.71 0.75 0.02 32 -0.28 2.40 -0.21 0.64 0.34 0.43 2.34 -0.65 33-0.28 -0.01 0.97 -1.57 -0.17 -1.74 -0.19 -1.19 0.33 34 0.47 -0.18 -1.47 0.54 0.22 0.00 0.53 0.37 0.79 -0.18 0.19 -1.01 0.13 350.12 0.27 0.69 -0.64 0.36 0.38 0.08 0.02 0.02 0.66 36 0.21 1.02
11 TABLE 5. OVERALL ASSESSMENT OF LABORATORIES PERFORMANCE (ZETA-SCORE) BY ELEMENTS Lab code AgAs Ca Cd CH3HgCo Cr Cu FeHgKLi MgMnNaPbRb SeSrVZn 1 0.73 0.90 0.17 -0.05 0.32 -0.23 0.58 -1.14 0.77 1.70 -0.52 2.74 0.20 1.15 2 0.03 0.71 1.10 0.84 3.45 0.82 -0.87 0.06 0.59 0.01 -1.50 0.54 0.51 1.04 0.85 3 4 -2.91 -0.25 -2.67 -2.02 -1.28 -1.56 5 1.07 0.71 1.11 0.20 -0.15 -2.51 0.00 -0.90 -5.87 -0.24 -0.75 -0.22 0.48 -0.20 0.96 6 -0.18 -1.58 -0.44 0.00 2.61 -0.13 -0.98 -1.43 7 -3.88 1.05 0.24 0.56 0.49 -0.12 -0.94 0.18 -2.14 0.49 0.14 1.72 1.14 -0.98 -0.36 1.96 0.48 0.13 8 0.81 -0.20 -0.84 -4.41 -1.17 0.14 0.26 -1.03 -1.10 0.60 -0.04 0.75 0.81 8B -0.66 9 -0.59 -0.64 -0.51 -0.72 -0.10 -1.20 -1.03 -0.11 -0.01 -1.22 -0.23 -0.56 -0.11 -0.58 -0.09 -0.05 -1.83 10 -0.06 -0.54 -1.24 0.00 0.22 -0.20 4.77 -1.64 12 0.10 -1.21 13-0.28 -0.38 0.35 -0.10 0.00 -0.09 -0.68 0.27 0.17 -0.14 0.15 -0.33 -0.50 0.74 14 -1.16 0.58 -4.42 10.31-1.52 -1.33 1.11 -0.73 0.43 -0.95 -0.62 0.38 15 0.20 0.50 1.02 1.64 0.21 -0.40 0.64 0.48 0.35 1.31 0.74 1.16 1.25 0.07 0.46 0.37 -0.06 0.31 0.86 16-0.46 -2.41 -0.62 0.67 -1.41 -1.56 0.65 0.42 -13.27 -1.07 -0.46 0.28 -0.42 -0.59 -1.59 -0.96 0.28 17 18 1.58 0.62 -0.08 -0.56 0.02 -0.41 3.21 1.26 2.86 2.83 0.22 0.65 190.18 0.34 1.03 -0.04 0.22 1.46 20 22A-1.48 0.12 -1.28 0.19 -0.40 -0.07 -1.44 -0.90 22B -4.99 2.86 -0.84 -1.73 -2.91 -3.88 23 1.10 -0.26 1.26 3.47 252.94 0.18 -1.13 0.65 -1.38 -1.21 -0.54 0.46 0.49 0.76 -1.46 0.43 264.74 3.26 0.98 4.41 3.80 1.44 -0.03 2.21 3.62 2.84 3.03 4.04 0.72 3.45 4.80 0.90 3.40
